1. Field of the Invention
The present invention relates to a machine tool including a sealing structure in a rotation unit.
2. Description of the Related Art
A sealing structure is provided in a rotation unit such as a main shaft of a machine tool in order to prevent the intrusion of an atmosphere including a cutting fluid or mist of the cutting fluid. The sealing structure may be formed as an oil seal or a labyrinth seal.
A rotation body sealing device disclosed in Japanese Utility Model Application Laid-Open (JP-U) No. 58-149655 prevents the intrusion of a cutting fluid or the like by providing a sealing structure in combination of a labyrinth seal and an air seal.
JP-U No. 62-185450 discloses a spindle motor that reinforces a sealing structure by complicating a shape of a labyrinth seal.
JP-U No. 4-90700 discloses an air sealing structure that reinforces a sealing structure by providing a multi-stage foreign matter intrusion prevention unit in addition to the combination of the labyrinth seal and the air seal.
FIG. 2 is a cross-sectional view illustrating the periphery of a rotation unit of a feeding shaft according to the related art. A shaft 1 is held by a bearing 2 and a housing 3. As a sealing structure, a labyrinth seal 4 and an air seal 7 are used together. The labyrinth seal 4 is formed between the shaft 1 and a plate-shaped shielding member 8. The shaft 1 is rotated by a power source such as a motor.
When the rotation unit rotates at a constant speed, the labyrinth seal 4 prevents the intrusion of the atmosphere including the cutting fluid or the mist of the cutting fluid with respect to the sealing structure. When the rotation unit stops, the air seal 7 prevents the intrusion of the atmosphere including the cutting fluid or the mist of the cutting fluid with respect to the sealing structure.
However, when the rotation unit enters a transition state as a deceleration state where a certain constant rotation number reaches a different constant rotation number, the labyrinth seal 4 suctions a gas in the periphery of the seal. At this time, a clean atmosphere supplied as the air seal 7 is first suctioned to the labyrinth seal 4.
Here, in the related art, there is a case where a clean atmosphere supply amount is smaller than an amount of the gas suctioned to the labyrinth seal since the fact that the labyrinth seal 4 suctions the peripheral gas in the transition state as the deceleration state is not known. As a result, since the clean atmosphere supply amount is not enough, the labyrinth seal 4 suctions the atmosphere including the cutting fluid or the mist of the cutting fluid along with the clean atmosphere for sealing air. Accordingly, the cutting fluid or the mist of the cutting fluid intrudes into the power source such as a motor.
FIG. 3 is a cross-sectional view illustrating the periphery of the rotation unit of the feeding shaft in which both an oil seal 5 and the air seal 7 are used as a sealing structure in the related art. The shaft 1 is held by the bearing 2 and the housing 3. In the oil seal 5, when the rotation number increases, the rotation unit and the oil seal are separated from each other, so that the sealing effect is degraded. At this time, the air seal 7 makes up for the sealing effect of the oil seal 5. However, in the case where the current state becomes the transition state where the constant rotation number reaches the different constant rotation number while the rotation unit and the oil seal 5 are separated from each other, there is a concern that the clean atmosphere supply amount is not sufficient due to the air seal 7 when the rotation unit and the oil seal 5 separated from each other return to the original state, and the atmosphere including cutting fluid or the mist of the cutting fluid is suctioned.
In general, the machine tool includes the sealing structure that is provided in the rotation unit so as to prevent the intrusion of the atmosphere including the cutting fluid or the mist of the cutting fluid. However, such a sealing structure is a sealing structure contrived based on the operation in the rotation state or the stop state, and is not contrived in consideration of the transition state from the rotation state to the stop state and the transition state from the stop state to the rotation state.
In fact, there is a case in which the atmosphere including the cutting fluid or the mist of the cutting fluid intrudes into the sealing structure in the rotation transition state as the deceleration state where the rotation unit changes from the rotation state to the stop state. The intruded cutting fluid has a bad influence such as poor lubrication of a bearing, and hence the reliability of the machine tool is degraded. Accordingly, the intrusion of the cutting fluid or the mist of the cutting fluid into the sealing structure may not be prevented only by the sealing structure contrived based on the operation in the rotation state or the stop state.